Gaofeng Ye

Three‐dimensional electrical structure of the crust and upper mantle in Ordos Block and adjacent area: Evidence of regional lithospheric modification

Long-period magnetotelluric (MT) data from project SINOPROBE were acquired and modeled, using three-dimensional (3D) MT inversion, to study the electrical structure of Ordos Block, a component of the North China Craton. For the first time, a high-resolution 3D resistivity model of the lithosphere is defined for the region. Contrary to what would be expected for a stable cratonic block, a prominent lithospheric conductive complex is revealed extending from the upper mantle to the mid-to-lower crust beneath the northern part of Ordos. Correlating well with results of seismic studies, the evidence from our independent magnetotelluric data supports regional modification of the lithosphere under the north Ordos and lithosphere thinning beneath Hetao Graben. The abnormally conductive structure may result from upwelling of mantle material in mid-to-late Mesozoic beneath the northern margin of the Ordos block.

Constraints on the evolution of crustal flow beneath northern Tibet

Crustal flow is an important tectonic process active in continent-continent collisions and which may be significant in the development of convergent plate boundaries. In this study, the results from multidimensional electrical conductivity modeling have been combined with laboratory studies of the rheology of partially molten rocks to characterize the rheological behavior of the middle-to-lower crust of both the Songpan-Ganzi and Kunlun terranes in the northern Tibetan Plateau. Two different methods are adopted to develop constraints on melt fraction, temperature, and crustal flow velocity in the study area. The estimates of these parameters are then used to evaluate whether crustal flow can occur on the northern margin of the Tibetan plateau. In the Songpan-Ganzi crust, all conditions are satisfied for topography-driven channel flow to be dominant, with partial melt not being required for flow at temperature above 1000°C. Further north, the Kunlun fault defines the southern boundary of a transition zone between the Tibetan plateau and the Qaidam basin. Constrained by the estimated melt fractions, it is shown that channel injection across the fault requires temperatures close to 900°C. The composition of igneous rocks found at the surface confirm those conditions are met for the southern Kunlun ranges. To the north, the Qaidam basin is characterized by colder crust that may reflect an earlier stage in the channel injection process. In the study area, at least 10% of the eastward directed Tibetan crustal flow could be deflected northward across the Kunlun Fault and injected into the transition zone defining the northern margin of the Tibetan plateau.

Application of Wireless Communication Technology in Geophysical Instrument

Geophysical instruments with high precision and resolution have become an important way during the development of geophysics. Some experts use modern electronic technology and computer technology into geophysical instrument. However, there are few papers on the application of wireless communication in geophysical instrument. This paper shows a kind of geophysical instrument, which is based on wireless communication and consists of data acquisition unit, data coordinator unit and computer. All the data acquisition units acquire the parameters and pass them to the data coordinator unit via wireless communication and the data coordinator unit collects the data, pass them to the computer finally. The system accomplishes the wireless communication with CC1100, a chip of Chipcon. This paper introduces the structure of the system and makes detailed explanation of the design.

Synthesis of natural electric and magnetic Time‐series using Inter‐station transfer functions and time‐series from a Neighboring site (STIN): Applications for processing MT data

Synthesis of natural electric and magnetic Time-series using Inter-station transfer functions and time-series from a Neighboring site (STIN) is a new approach for recovering natural electric and magnetic fields and reduce the influence of anthropogenic noise. The proposed approach modifies the windows of the local electric and magnetic time-series that are affected by noise with time series resulted from modifying the spectra of the magnetic time-series from a neighboring site with the inter-station transfer functions between the local and neighboring sites. The STIN method was tested with artificially contaminated electric and magnetic time-series. Comparison between STIN-corrected time-series and original non-contaminated time-series shows high similarity, both in the time and frequency domains. Differences were quantified using the normalized root-mean-square error, the correlation coefficient, and the signal to noise ratio. The STIN method was also applied to two sites affected by unconstrained anthropogenic noise, thus demonstrating the ability and accuracy of STIN in synthesizing natural electric and magnetic fields and reducing the influence of anthropogenic noise. The synthesized time-series provided by STIN show the method to be valuable for MT geophysical applications, by increasing the reliability when constrains the MT impedance tensor, and by reducing the scatter of data points when the time-series are affected by noise, particularly for longer periods. As STIN is based on inter-station transfer functions, the electric and magnetic time-series can be treated independently, enabling computation of the MT impedance tensor even when the electric and magnetic time-series of the local site were recorded at different times.